Incubation of Eggs

New Zealand Journal of Agriculture, Volume 87, Issue 1, 15 July 1953, Page 16

Incubation of Eggs

THE most important requirement in a good hatching egg is that it shall have been produced, from well-bred stock. However faultless treatment of it after it has been produced may be, nothing can be done to improve the quality of an egg from a poor bird. It is in the breeding pen and not in the incubator room that first efforts must be made toward producing the perfect chick. But hatchability even of eggs from good stock can be reduced by shortcomings in incubator management, and some of the essentials in successful incubation practice are considered in this article by J. H. Jones, Poultry Instructor, Department of Agriculture, Christchurch.

NESTS must be kept as clean as possible. An egg cools after it has been laid, the contents tend to shrink, a slight vacuum forms inside the egg, and through the porous shell moulds or bacteria may be drawn. The cleaner the nesting material is the less chance there is of the eggs becoming infected. Eggs for hatching should not be washed. Washing tends to spread the dirt or infection over the whole area of the shell, whereas originally it may have covered only a small portion. Eggs should be gently scraped with a dry knife. The ideal time for an egg to be set would be immediately it has been laid, though there would be very little effect from keeping it until after the seventh day. Eggs kept for more than a fortnight take longer to hatch than fresh ones. The holding of eggs should be practised as little as possible even under the best conditions. The ideal temperature appears to be between 50 and 55 degrees F. For short periods low temperatures will have less harmful effects than high temperatures, which will cause cell division. In eggs held for prolonged periods at either higher or lower temperatures than 60 and 40 degrees respectively the germs

tend to die during the first few days of incubation. It is thought that the embryonic development that is under way at the time when the egg is laid should be halted as soon as possible, and for this reason it is advisable to collect eggs frequently, say two or three times a day. During holding of eggs there is a slight loss of weight due to evaporation, but the most important effect is the weakening of the life-germ. The air in the storage room should be fresh and free from strong currents or odour. Eggs should be placed on racks with the large end uppermost, and if they are set. on or before the seventh day will not require to be turned. After a week it is advisable to turn them daily; otherwise the germinal disc, which by force of gravity always rides on top of the yolk, will gradually tend upward through the layer of albumen toward the shell membrane, to which it may become attached owing to the continual slight evaporation of water from the surface of the shell. Precaution when Setting Eggs When the eggs are set it is important to watch that the temperature of the incubator is not greatly reduced for too long a period through too many

trays of cold eggs being put in. If the temperature is reduced to 90 degrees F., it may take 5 or 6 hours to warm up again to 100 degrees and at this early and critical stage this may have a weakening effect on the embryos and may even cause some to fail to hatch. A few trays at a time should be put in to reduce as much as possible this loss of heat. Ventilation Ventilation should receive the closest attention. Lack of proper oxygen supply will be accompanied by an increase in the proportion of CO 2 (carbon dioxide), which will affect the mortality rate if present in quantities above 180 parts in 10,000 in the air. The greater the porosity of the shells the more likely are the embryos to die from this cause. The fact that porosity may vary such a great deal accounts for the fact that bad ventilation does not have a uniform effect over the whole hatch, as would temperature, for instance. During power cuts it is usual to close down the vents, and this is not harmful provided they are opened again immediately the power comes on. Unfortunately it is easy to forget to reopen vents, and such neglect may cause a small percentage reduction in the hatch. The amount of CO 2 produced by each egg in the incubator is very large in proportion to its sizeabout 5-j pints in 17 days. Where hundreds of eggs are involved ventilation must be very efficient to keep the air sweet. Inside the incubator this is the business of the manufacturer, but the air in the incubator room must be changed often

enough to be able to feed the necessary oxygen into the incubator. Cowls operate under the influence of the wind, which causes the air to be sucked out through the roof. For these to work effectively the incubator house must be in a position where the wind is not obstructed, as by tall hedges or high buildings. Otherwise an extractor fan must be - used, but this is more costly. The air inlets should be placed as far as possible away from the cowls or extractor; that is, as low as can be arranged and at the farthest end of the room, so that the room will not be bypassed by the air. Inlets should be baffled to prevent direct draught. If the ventilation is efficient, the incubator room will not feel stuffy after having been shut up overnight. If the farmer feels the air oppressive or if there is any tendency to headaches after he has worked there all day, matters should be investigated. The extractor fan has the advantage that its speed may be regulated. More air changes may be necessary in warmer weather. Best Temperature for Development The temperature at which the egg will develop best is 100 degrees. In cabinet type machines this applies of course to the whole incubator, and the air is uniform in temperature, as nearly as possible. In the table type machine there is a graduation in temperature from the source of heat at the top to the bottom of the eggs of 4 or 5 degrees, and under the hen there is a variation of as much as 12 degrees, but in each instance the temperature at the centre of the egg is about 100 degrees. Although fluctuations from this optimum temperature always to some

extent upset the even rhythm of development of the embryo, the time at which most harm will be done is in the early stagesin the first 48 hours. As turning in the table type machines means that the eggs will be cooled, they should not be. turned during the first 48 hours. In cabinet machines they should be turned as usual. Humidity Range During the period of incubation the egg normally loses from 10 to 13 per cent, of its moisture, and some extra humidity will be required so that the loss shall not be excessive owing to the evaporation which takes place due to frequent changing of the air. For most eggs a wet bulb reading of 85 degrees (55 per cent, humidity) is. found to give the best results. If, however, it is known that a batch of eggs has thick shells and low porosity, humidity may be reduced with advantage to say 52 per cent. (84 degrees). Eggs having thin shells should not be set. Temperature and humidity must be considered together, because one affects the other. Too low a humidity may cause excessive evaporation and reduce the temperature of the eggs below 100 degrees even when the dry thermometer shows that temperature. Humidity is often increased while the hatch is in progress, with good results, but the chickens should not be allowed to remain in this atmosphere well into the twenty-second day, as sometimes happens when they await the sexer or the customers. The high humidity will cause the actual temperature to exceed 100 degrees and may have a serious effect on the chicks. The humidity should be

brought back to normal once the chicks are hatched. Turning Eggs In cabinet incubators it is found that little is to be gained from turning the eggs oftener than 5 times in 24 hours, although there are machines on the market that turn eggs automatically at hour intervals. In table type machines after the first 2 days eggs are usually turned twice a day and sometimes three times. To turn them oftener would reduce the temperature too greatly. ’ They should be given a half turn on to their opposite sides each time. Turning in the early stages helps to prevent the yolk from adhering to the shell membrane by riding up through the albumen. During the later stages turning helps to prevent the various embryonic membranes from adhering to one another and helps the embryo to take up its correct position within the shell. Normally the chick’s head should be in the large end and the chick should be curled up so that its beak is in a position easily to peck through the shell. In about 25 per cent, of eggs there is a tendency for the chick to develop in the wrong position, and this may be rectified by frequent turning. A great deal of study has revealed the stages in the development of the chick from the egg, but the why and wherefore of it still remain a mystery. Poultrymen are concerned with making this phenomenon take place as smoothly as possible by careful attention to its exacting requirements. Success in this, as in any other venture on the farm, cannot be bought cheaply, but comes only through infinite attention to detail. .

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